Field of the Invention
The present invention relates to a method and system for providing hearing assistance to a user, wherein audio signals from a microphone for capturing a speaker's voice are transmitted via a wireless link to a receiver unit, such as an audio receiver for a hearing aid, from where the audio signals are supplied to means worn at ear level for stimulating the hearing of the user, such as a hearing aid loudspeaker.
Description of Related Art
The wireless audio link of hearing assistance systems often is an FM (frequency modulation) radio link operating in the 200 MHz frequency band. In recent systems the analog FM transmission technology is replaced by employing digital modulation techniques for audio signal transmission, most of them working on other frequency bands than the former 200 MHz band.
U.S. Patent Application Publication 2005/0195996 A1 relates to a hearing assistance system comprising a plurality of wireless microphones worn by different speakers and a receiver unit worn at a loop around a listener's neck, with the sound being generated by a headphone connected to the receiver unit, wherein the audio signals are transmitted from the microphones to the receiver unit by using spread spectrum digital signals. The receiver unit controls the transmission of data, and it also controls the pre-amplification gain level applied in each transmission unit by sending respective control signals via the wireless link.
International Patent Application Publication WO 2008/098590 A1 relates to a hearing assistance system comprising a transmission unit having at least two spaced apart microphones, wherein a separate audio signal channel is dedicated to each microphone, and wherein at least one of the two receiver units worn by the user at the two ears is able to receive both channels and to perform audio signal processing at ear level, such as acoustic beam forming, by taking into account both channels.
International Patent Application Publication WO 2010/078435 A1 and corresponding U.S. Pat. No. 8,150,057 relate to a communication system comprising a plurality of transmission units comprising a microphone for capturing the respective speaker's voice and transmitting audio signal data packets to a receiver unit which may be connected to an earphone or to a hearing aid via a plug jack. The transmission units and the receiver unit form a wireless network.
One type of hearing assistance systems is represented by wireless systems, wherein the microphone arrangement is part of a transmission unit for transmitting the audio signals via a wireless audio link to a receiver unit comprising or being connected to the stimulating means. Often in such systems the wireless audio link is an narrow band FM radio link. The benefit of such systems is that sound captured by a remote microphone at the transmission unit can be presented at a much better SNR to user wearing the receiver unit at his ear(s).
According to one typical application of such wireless audio systems, the stimulating means is loudspeaker which is part of the receiver unit or is connected thereto. Such systems are particularly helpful in teaching environments for normal-hearing children suffering from auditory processing disorders (APD), wherein the teacher's voice is captured by the microphone of the transmission unit, and the corresponding audio signals are transmitted to and are reproduced by the receiver unit worn by the child, so that the teacher's voice can be heard by the child at an enhanced level, in particular with respect to the background noise level prevailing in the classroom. It is well known that presentation of the teacher's voice at such enhanced level supports the child in listening to the teacher.
According to another typical application of wireless audio systems the receiver unit is connected to or integrated into a hearing instrument, such as a hearing aid. The benefit of such systems is that the microphone of the hearing instrument can be supplemented or replaced by the remote microphone which produces audio signals which are transmitted wirelessly to the FM receiver and thus to the hearing instrument. In particular, FM systems have been standard equipment for children with hearing loss in educational settings for many years. Their merit lies in the fact that a microphone placed a few inches from the mouth of a person speaking receives speech at a much higher level than one placed several feet away. This increase in speech level corresponds to an increase in signal-to-noise ratio (SNR) due to the direct wireless connection to the listener's amplification system. The resulting improvements of signal level and SNR in the listener's ear are recognized as the primary benefits of FM radio systems, as hearing-impaired individuals are at a significant disadvantage when processing signals with a poor acoustical SNR.
European Patent Application EP 1 691 574 A2 and corresponding U.S. Patent Application Publication 2006/0182295 relate to a wireless system, wherein the transmission unit comprises two spaced-apart microphones, a beam former and a classification unit for controlling the gain applied in the receiver unit to the transmitted audio signals according to the presently prevailing auditory scene. The classification unit generates control commands which are transmitted to the receiver unit via a common link together with the audio signals. The receiver unit may be part of or connected to a hearing instrument. The classification unit comprises a voice energy estimator and a surrounding noise level estimator in order to decide whether there is a voice close to the microphones or not, with the gain to be applied in the receiver unit being set accordingly. The voice energy estimator uses the output signal of the beam former for determining the total energy contained in the voice spectrum.
It is generally known to provide hearing assistance systems with a voice activity detector (VAD) in order to recognize when a speaker's voice is present close to the microphone of the hearing assistance system or not, so that the gain applied to the audio signal is captured by the microphone can be adjusted accordingly; typically, the gain is reduced during times when no close voice is detected in order to avoid unpleasant perception of noise signals.
U.S. Pat. No. 4,696,032 relates to a hearing aid wherein the gain is controlled by the output of a VAD.
U.S. Pat. No. 6,101,376 mentions that FM radio systems may have a manually adjustable squelch, wherein only input signals are passed to the speaker when the input level exceeds an adjustable threshold level.
European Patent Application Publication EP 0 483 701 A2 relates to a hearing aid comprising a soft squelch function, wherein the gain is automatically reduced for low input signal levels.
International Patent Application Publication WO 2010/133703 A2 and corresponding U.S. Pat. No. 9,131,318 relate to hearing assistance system comprising a wireless microphone, wherein the knee-point of the gain curve, i.e. the gain vs. input speech level, is adjusted as a function of the ambient noise level in such a manner that the knee-point is shifted to lower values for low ambient noise levels, i.e. the gain is increased at low ambient noise levels.
International Patent Application Publication WO 2008/138365 A1 and corresponding U.S. Pat. No. 8,345,900 relate to a FM wireless microphone hearing assistance system particularly suited for school applications and comprising a VAD and a surrounding noise level estimation unit in the audio signal transmission unit, wherein in addition to the audio signals control data is sent to the ear level receiver unit so that a gain control unit of the receiver unit selects the gain according to whether the transmission unit is in the “voice on” regime or in the “voice off” regime. In the “voice off” regime the gain is reduced by a fixed attenuation factor (such as 20 dB) compared to the “voice on” regime. An additional gain off-set depending on the estimated surrounding noise level is applied in both regimes, with the gain off-set being the same in both regimes. Thus, the gain is always reduced by e.g. 20 dB—irrespective of the surrounding noise level—when the VAD detects that the speaker stops talking. A similar system is described in European Patent Application Publication EP 1 863 320 A1.
European Patent Application Publication WO 2010/000878 A2 and corresponding U.S. Pat. No. 8,831,934 relate to a speech enhancement system comprising a wireless microphone for a loudspeaker arrangement placed in a room, wherein the gain is selected as a function of the ambient noise level in order to implement a “surrounding noise compensation” (SNC). The system comprises a VAD and an ambient noise estimator for determining the surrounding noise level during times when the VAD signal indicates that the speaker is not speaking. During times, when the VAD signal indicates that the speaker is speaking, the gain is increased, until the ambient noise level is expected to be masked by the late reverberation level.